Preparation of alkali metal aluminum hydrides

ABSTRACT

A process for preparing alkali metal aluminum hydride comprising reacting together an alkali metal, or the hydride thereof, with aluminum having alloyed therewith either Ti or Zr, under hydrogen pressure in the presence of a tertiary amine. Preferably, the catalyst comprises a tertiary amine and a hydrocarbon compound which is capable of being metallized under the reaction conditions, such as triphenylmethane, indene, thiophene, fluorene, and alpha-picoline. Reaction times are reduced to about one-third normal and provides for recycling the catalysts and reaction media in which the reaction is conducted. Sodium aluminum hydride prepared by this method is a good source of high-purity hydrogen for use in fuel cells and the like. Reaction temperatures range from 50* C. to 200* C. under pressures of from 500 to 10,000 pounds per square in (p.s.i.).

United States Patent 72] Inventors [21 Appl. No. [22] Filed [45]Patented [73] Asaignee [54] PREPARATION OF ALKALI METAL ALUMINUMHYDRIDES 9 Claims, No Drawings [52] 11.8. 23/365 [51] Int.

C0lb 6/24 [50] Field of Search 23/361, 365. 204; 260/448; 252/428,431

[56] References Cited UNITED STATES PATENTS 3,357,806 12/1967 Dvorak etal. 23/365 3,387,949 6/1968 Snyder 23/365 FOREIGN PATENTS 45,701 11/1966Germany 23/365 756,510 4/1967 Canada 23/365 OTHER REFERENCESZak1arkin,"L. T. et a1,; Academy of Sciences USSR,

Proceedings Chemical Section; Volume 145, 1962 pp. 656- 57.

Ruff, John K. et al.; Journal of the American Chemical Society, Vol.83,Feb. 196l,pp.535- 38 Ashby, E. C. et al.; inorganic Chemistry," Vol.2, No. 3, 1 June 1963, pp. 499 503 Primary Examiner-Oscar R. VertizAssistant Examiner-G. O. Peters Attorney-Donald L. Johnson ABSTRACT: Aprocess for preparing alkali metal aluminum hydride comprisingreactingtogether an alkali metal, or the hydride thereof, with aluminum havingalloyed therewith either Ti or Zr, under hydrogen pressure in thepresence of a tertiary amine. Preferably, the catalyst comprises atertiary amine and a hydrocarbon compound which is capable of beingmetalliz'ed under the reaction conditions, such as triphenyl-' methane,indene, thiophene, fluorene, and alpha-picoline. Reaction times arereduced to about one-third normal and provides for recycling thecatalysts and reaction media in which the reaction is conducted. Sodiumaluminum hydride prepared by this method is a good source of high-purityhydrogen for use in fuel cells and the like. Reaction temperatures rangefrom 50 C. to 200C. under pressures of from 500 to 10,000 pounds persquare in (p.s.i.

PREPARATION OF ALKALI METAL ALUMINUM HYDRIDES BACKGROUND OF THEINVENTION 1 Field of the Invention This invention relates to a methodfor preparing alkali metal aluminum hydrides having the formula MAlH,wherein M comprises an alkali metal. More particularly, the inventionrelates to a method for preparing sodium aluminum tetrahydride.

2. Description of the Prior Art A method of preparing sodium aluminumhydride directly from the elements is the subject of pending US. Pat.application Ser. No. 7$l,862, filed July 30, 1958, owned by the assigneeof the present application. Generally, the method comprises contactingsodium, or sodium hydride, and aluminum with "hydrogen, at elevatedtemperatures and pressures, producing sodium aluminum hydride in goodyields. One use for the sodium aluminum hydride produced thereby is as asource of hydrogen for certain applications such as fuel cells.

Efforts are continuing to increase the efficiency of fuel cells using asa hydrogen source sodium aluminum hydride. "has been discovered that thelevel of hydrocarbon contaminants present in the hydrogen generated fromthe sodium aluminum hydride has a pronounced effect on the efficiency offuel cells.

In addition to the above, known processes of preparing alkali metalaluminum hydrideinvolve reaction times at least about 16 to 30 hours. Ina commercial operation, such lengthy reaction periods are unacceptable.For example, see U.S.

3,290,123, to Del Giudice et al., wherein reaction times are reported tobe at least about 16 hours at a temperature ofv about 1.75 C. withcontinuous agitation.

The present invention provides a process for producing alkali metalaluminum hydrides which overcome these and related disadvantages of theprior art.

SUMMARY OF THE INVENTION We have discovered a novel method of producingalkali metal aluminum hydride from which can bev generated.

hydrocarbon-free, high-purity hydrogen. in addition, reaction times aredrastically reducedrover those presently known in the art. The methodcomprises reacting together an alkali metal, or the hydride thereof, andaluminum, the aluminum having alloyed therewith either titanium (Ti) orzirconium: (Zr), with hydrogen, under elevated temperatures andpressures, in the presence of a tertiary amine. Preferably, the catalystcomprises (1) a tertiaryamine and (II) a hydrocarbon compound which iscapable of being metallizedlunder the, reaction conditions, such astriphenyl methane, indene,

zirconium (Zr), in an inert liquid reaction medium in thepresence ofhydrogen under superatrnotpheric pressure, in the presence of acatalystsystem consisting essentially of 1,4- diazabicyclo( 2.2.2)octane and a compound such as triphenylmethane, indene, fluorene,thiophene, alpha-picoline, and the like, while agitating the mixtureuntil the reaction between aluminum, hydrogen, and the alkali metal, orhydride thereof, is substantially complete, as evidenced by thecessation of hydrogen uptake.

in a continuous process, it would not be necessary for the reaction togo to completion. However, in batchwise preparations, it is customary toconduct the reaction until hydrogen pressure remains constant,evidencing no consumption thereof in the reaction.

The reaction proceeds as follows:

(tertiary amine) -A1H +MH (tertiary amine+z+u) M(AlH4) recycled whereinM isan alkali metal; x is a compound selected from the group consistingof triphenylmethane, fluorene, indene, thiophene, alpha-picoline, andthe like; and y is a suitable reaction media, preferably one in whichthe formed alkali metal aluminum hydride is insoluble. The reaction isconducted at a temperature of from about 50 C. to about 200 C. and atpressures ranging from about 500 to about 10,000 p.s.i.

The reaction product of equation (I) is stable only for a timesufficient to allow formation of sufficient quantities of the alkalimetal hydride to convert the tertiary amine. AIH, complex to the alkalimetal aluminumhydride. The alkali metal hydride being a stronger basethan the tertiary amine, the metal hydride replaces the amine in thecomplex, freeing the tertiary amine to be recycled in a continuousprocess, along with the reaction medium and othercatalyst components.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Known processes for preparingalkali metal aluminum hydride utilize aluminum in finely subdividedform. The particles generally range from birdshot size'down to a finelydivided powder. The powder should pass througha 325-mesh screen to theextent of about 80 percent thereof. When largesize pieces of aluminumare used, it is necessary to ball, mill, or grind the aluminum toachieve acti a i n.

However, in the known processes, activation of aluminum was usuallyaccomplished by the use of an aluminumalkyl. The use of aluminum alkylshas been found to contaminate the alkali metal aluminum hydrideresulting in a product from which evolved: hydrogen contained unwantedand harmful hydrocarbonsi Therefore, the present invention shouldutilize an aluminum powder, at least- 80 percent of which passes througha 325- mesh screen. ltis generally unnecessary to activate the aluminumby the old methods when the powder is used.

To achieve'theaccelerated reaction times, the aluminum powder shouldcontain either Ti or Zr, alloyed therewith. The Ti and/Zr may be presentas alloyed impurities in the aluminum, or may be incorporated in thealuminum by known carbothermic reduction means. The amount of Ti or Zrcomponent useful in reducing reaction times ranges from about 50 toabout 20,000 parts per million (p.p.m.) based on the weight of thealuminum powder. Preferably, the Ti or Zr component should be present ata level of at least 1,000 p.p.m.

The reaction may be conducted at a temperature between about 50 C. and200 C. and at a hydrogen pressure between about 500 and 10,000 poundsper square inch (p.s.i. A more preferable temperature range is betweenabout l00 to about 180" C., the most preferred temperatures rangingbetween about to about C. Preferred pressures for the invention rangebetween l,500 to about 4,500 p.s.i., with the most preferredrangingbetween about L500 to about 3,000 p.s.i.

Suitable inert liquid carriers are liquid hydrocarbons, such as hexane,trimethyl hexane, octane. toluene. benzen adecane, o-xylene, dodecane,and cyclohexane; the lower alkyl ethers, such as dimethyl ether. diethylether. diiosopropyl ether, and dibutyl ether; and other ethers, such astetrahydrofuran. dioxane, and dimethyl ether of diethylene hydridesthereof, such as sodium, potassium, rubidium and cesium. However, themost preferred alkali metals are sodium and potassium. When sodium isused, it may be in any suitable form since it is molten at reactiontemperatures. The mole ratio of alkali metal to aluminum is preferablyabout 0.913 to about 1.1:1. A slight excess of alkali metal is mostpreferred, although not absolutely necessary. An excess of aluminumpresent invention are sufficiently stable in air to allow charging of areactor without the complicated use of inert atmospheres. Analysis ofthe ultimate hydrogen product of the invention by mass spectrometricmeans reveals no detectable methane-6.0.

may be used if desired. However, the most suitable mole ratio 5 hy r nPresent thereinis from about 1:1 to about 1.1:1. The benefits andadvantages of the present invention are it has been found that alkalimetal aluminum hydride capamore readily understood in the followingexamples which are ble of evolving hydrocarbon-free, high-purityhydrogen may merely illustrative and are not intended to limit the scopeof be prepared by using as a catalyst a tertiary amine. Various theinventiontertiary amines have been found to be especially useful forthis purpose, such as, trimethyl amine, triethyl amine, triethylene EXA1 z l h i efhylene f h h qumolme In preparing sodium aluminumtetrahydride, 14 g. of aluan e ike. T e methylene diaminc is more p p 15minum powder which contains 2,000 p.p.m. Ti, and 12 g. of identified asl,4-diazabicyclo(2.2.2) octane, and has been Sodium metal were placed ina 250 Magne 5tir reactor fund be the most Preferable y amine in thePresent fitted with a magnetic stirrer and suitable heating means.inventionh diazaeoinpound is e conveniently called About 100 ml.predried toluene was used as an inert carrier Dabco and will be ftehtefetted to here"! by that namefor the reaction. In addition, there wasadded to the reactor 3 Dabco is readily available from severalmanufacturers, one wt. percent of l,4-diazabicyclo(2.2.2) octane and 6wt. per- Of which is the Aldrich Chemical mp y. it is cent oftriphenylmethane, weight percent being based on total ployed in theinvention in an amount ranging from about 0.1 metals charged. Hydrogenwas introduced into the reactor to about 10 weight percent, based on thetotal weight of alkali until the pressure reached about 2,500 p.s.i. Thetemperature metal and aluminum metals charged to the reactor. It is mostof h e r was main in at about 6 throughout h beneficial to use fromabout 3.0 to about 7.5 weight percent of entire run, fVith eontiniioilsagitation of the teactot- Pressure the Dabco, since satisfactory yieldsof alkali metal aluminum maintained by addmoh hydrogen when the pressurehydride and reaction rates are obtainable at this level of use. pp to atleast 2,090 P- The total hydt'ogen P In addition to the advantages ofusing a tertiary amine as the drop was recordeh dunhg the f whenhxdrogeh uplmkc sole catalyst of the invention, it has been found thateven 0 ceased rcahhoh was z h g eshseghahy T i. better results areobtainable when the tertiary amine is used in 3 Tom] macho" time was 7 hy when up e o about 2,700 pounds. Sodium aluminum hydride wascombination with a cocatalyst material. A cocatalyst which 15 h f93uitable for use with the tertiary amines of the invention is recoveredatayleld ofover 90 pefcem a pumy 0 s I d f h f h cent. The sodiumaluminum hydride recovered was treated so Se 6cm mm t e 0 ehylmethahe asto evolve hydrogen. The hydrogen evolved was collected dene, fluorene,thiophene, alpha-plcoline, and the bite. T and analyzed by massspectrographic means with the amount most preferred cocatalyst, due toits ease of handling and ofcarbon compounds present b i d ined, It wasfound availability, is triphenylmethane. The specific examples of thatno d bl carbon om ound was present therein. cocatalyst useful in theinvention are only representative of a large number of acidichydrocarbons that would be equally 40 EXAMPLE 2 useful. Generally, anyhydrocarbon compound capable of being metallized under the reactionconditions would be A chatge Similar to h in example was "f to a 9equany Suimble harem The cocatalyst has been found to be Magna-Stirreactor which was fitted with a stirrer and suitable useful at a levelof from about 0.1 to about 10 weight percent, heahhg means In place ofthe toluene t was added the based on total charged metals. Mostbeneficial results are ob- 100 of E550 S91v3 75 (a whne.oln' aummum vcontained 2,000 p.p.m. TI. The mole ratio of sodium to alutained whenthe cocatalyst 15 used in an amount ranging from minum was 1.1 to 1 andthe weight percent of Dabco was about 0.1 to about 7.5 weight percent.

A anicularl ad a ta r f t l t reduced from 3.0 percent to 2.0 percent.The reactor was p 4 i geous com ma 0 ca 8 5 compressurized with hydrogento a level of about 4,500 p.s.i. pnses (a) h myclouz'z) octhhe (b)mphehyl' The reaction was essentially complete after 3.0 hours, with hIn to the combmahm (a) and i 3,400 pounds of H, being consumed, yielding92 percent heremabove, it has been found that good results are obtama- 1The sodium aluminum d id recovered was hie e Dlabco is Combined withaipha'pieoiihe it! adtiitiohy rified by recrystallization intetrahydrofuran (THF) and p 'p alone. is effective in catalyzing thei'eaetion of treated with water to release the hydrogen. Analysis of thethe Present inventinevolved hydrogen revealed no detectable hydrocarbonsUsing the above amounts of catalyst, rates of reaction have re enttherein, been found to be as good as or better than when aluminumalkyls, such as triethyl aluminum, were used as catalysts. in ad-EXAMPLES 3-13 l h 'h L; analysts are thehreguhmg Additional runs weremade varying the weight percent of a a meta hh y n 6 may pro uce a ymgeh Dabco and alternating the cocatalysts. The preparations wereproduct mahhhg some hydrocarbons such as made using varying hydrogenpressure, but maintaining the ethanol, and butanes. Even moreadvantageously. uti same general temperature range. A Magna-Stir reactorwas of the catalyst system of the invention avoids the inherent employedf each preparation Th genera] procedure d pr ss pr l m attending th 0fPYI P C Such as in examples 1 and 2 were used throughout. The resultsare in aluminum alkyls. All of the reactants used in the process ofthetable 1.

- TABLEI V A1 Dabco Hz Hydrogen Reaction Alkali Amount amount (weightcocatalyst pressure Temp. Reaction Yield analysis time Example metal(gms) (gms) percent) (weight percent) (p.s.i.) C.) medium (percent)(p.p.m.) (hrs.)

12 14 3.0 Triphenyl 2,500 'Ioluene.. 93 Pure 24 14 methane-8.0. 2 000 812 l 12 ta; 15 14 a-PiCOHIle-9.0 2',500 21 14 3.0 Triphenyl 2,500 6Table l-Continued 9 K 21 14 2.0 Thiophene4.0 3,500 150 do 3 d H 6 10 Na12 14 4.0 Tnlphenyl 2,500 150 Trimethyl 93 do 7 methane-7.5. hexzne. 11Na 12 14 1.0 Triphenyl 2, 000 150 Octane 87 do 8 methane-2.0. 12b N 1214 Triethyl 2,000 140 To1uene 89 Ethane-496" 6 aluminum. {iltlganol-WQ}u she-85... 13 Na 12 14 3.0 2,500 145 do 76 Pure 7 a Weight percent ofcatalyst components based on total weight of metals charged. b Example12 is a run to illustrate hydrocarbon contaminants in H2 evolved fromthe NaAlHr produced p.p.m. Ti.

using a triethyl aluminum catalyst. The aluminum contained 2,000

Hydrocarbon contaminants measured in parts per million, on a volumebasis. 6 The aluminum used in Examples 313 contained the followingamounts of either Tl or Zr, the amount based on aluminum used: Example 310 p.p.m. Ti); 4 (1,900 p.p.m. Zr);

5 (20-50 p.p.m. Ti); 6-9 (2,000 p.p.m. Ti); 10 (200 p.p.m. Ti); 11 (300p.p.m. T1); 12 (2,000

p.p.m. Ti); and 13 (2,000 p.p.m. Ti).

tion of the fuel cell. Fuel cell life has been at least doubled usingthe products ofthis invention.

Having thus described the process of this invention, it is not intendedthat it be limited except as set forth in the following claims.

Whatis claimed is:

l. A process for producing alkali metal aluminum hydride capable ofevolving hydrocarbon-free hydrogen, which com prises reacting togetheran alkali metal and aluminum, at a mole ratio of from about 0.93 toabout 1.1:1, the aluminum containing from about 1,000 to about 20,000p.p.m. based on the aluminum present, of a metal selected from the groupconsisting of titanium and zirconium; with hydrogen at a pressure offrom about 1,500 psi. to about 4,500 p.s.i., and at a temperature offrom about 100 C. to about 180 C., in the presence of (l) a catalystconsisting essentially of (a) from about 0.1 to about 10 weight percent,based on the total weight of alkali metal and aluminum, of1,4-diazabicyclo(2.2.2)octane and (b) from about 0.1 to about 10 weightpercent, based on the total weight of alkali metal and aluminum, of acompound selected from the group consisting of triphenylmethanc, indene,thiophene, fluorenc, and alpha picoline, and (11) a liquid hydrocarbonreaction medium; and recovering solid, crystalline alkali metal aluminumhydride from said reaction medium.

2. The process of claim 1 wherein the aluminum has at least 1,000 partsper million titanium alloyed therewith.

3. The process of claim 1 wherein the alkali metal aluminum hydride isprepared by reacting together sodium and aluminum, in a mole ratio offrom about 1:1 to about 1.1:], the aluminum containing about 2,000 partsper million titanium;

' percent of triphcnylmethane, the amount of catalyst being based on thetotal metals present in the reaction, and (ll) a reaction mediumconsisting essentially of toluene; and recovering solid, crystallinesodium aluminum hydride from said toluene.

4. A cyclic process for preparing an alkali metal aluminum hydridecapable of evolving high purity, hydrocarbon-free hydrogen; whichcomprises conducting the reaction of claim 1, separating from thereaction medium the alkali metal aluminum hydride and recycling thereaction medium and catalyst components in a continuous process forpreparing the alkali metal aluminum hydride.

5. The process of claim 1, wherein the alkali metal is sodium.

6. The process of claim 4 wherein the alkali metal is sodium.

7. The process of claim 4 wherein the alkali metal aluminum hydrideproduced thereby is sodium aluminum hydride.

8. The process of claim 1, wherein said catalyst is present in thereaction system in an amount ranging from about 3.0 to about 7.5 weightpercent, based on the total weight of alkali metal and aluminum chargedto the system.

9. The process of claim 1 wherein said liquid hydrocarbon reactionmedium is toluene.

2. The process of claim 1 wherein the aluminum has at least 1, 000 partsper million titanium alloyed therewith.
 3. The process of claim 1wherein the alkali metal aluminum hydride is prepared by reactingtogether sodium and aluminum, in a mole ratio of from about 1:1 to about1.1:1, the aluminum containing about 2,000 parts per million titanium;with hydrogen at a pressure of from about 1,500 to about 4,500 p.s.i.and at a temperature of from about 140* to about 170* C., in thepresence of (I) a catalyst consisting essentially of (a) from about 3.0to about 7.5 wt. percent of 1,4-diazabicyclo(2.2.2)-octane and (b) fromabout 0.1 to about 7.5 wt. percent of triphenylmethane, the amount ofcatalyst being based on the total metals present in the reaction, and(II) a reaction medium consisting essentially of toluene; and recoveringsolid, crystalline sodium aluMinum hydride from said toluene.
 4. Acyclic process for preparing an alkali metal aluminum hydride capable ofevolving high purity, hydrocarbon-free hydrogen; which comprisesconducting the reaction of claim 1, separating from the reaction mediumthe alkali metal aluminum hydride and recycling the reaction medium andcatalyst components in a continuous process for preparing the alkalimetal aluminum hydride.
 5. The process of claim 1, wherein the alkalimetal is sodium.
 6. The process of claim 4 wherein the alkali metal issodium.
 7. The process of claim 4 wherein the alkali metal aluminumhydride produced thereby is sodium aluminum hydride.
 8. The process ofclaim 1, wherein said catalyst is present in the reaction system in anamount ranging from about 3.0 to about 7.5 weight percent, based on thetotal weight of alkali metal and aluminum charged to the system.
 9. Theprocess of claim 1 wherein said liquid hydrocarbon reaction medium istoluene.